1. Field of the Invention
This invention relates generally to an inductive type magnetic thruster, and more specifically, to a pulsed inductive type magnetic thruster incorporating a plurality of parallel-connected one-turn coils for use as an engine in a space vehicle.
2. Discussion
Rocket engines for long term space exploration must meet demanding requirements that may not be as crucial in their present short term counterparts. Currently, experimentation is being conducted into developing engines that will meet the necessary requirements for long duration missions. Considerations include that the components of the engine be extremely durable and reliable. Also, high rocket exhaust velocity is necessary to reduce fuel requirement in order to achieve high useful payloads. These requirements provide a challenging avenue for engineers developing such engines.
Different types of designs have been experimented with over the course of the development of this technology. Generally, chemical propulsion engines are required to provide the initial launch function of a rocket because of their high thrust-to-mass ratios. However, chemical rockets typically exhibit a low propellant exhaust velocity, usually referred to as specific impulse (I.sub.sp) Therefore, other types of engines that do not require the generation of heat for propellant acceleration have been experimented with to provide the high I.sub.sp necessary for sustained long term space travel. Specifically, certain electric type engines are known which use either electric fields (Ion Engine) or magnetic fields (direct-current, electrode type engines) for propulsion. However, these types of engines have typically met with various drawbacks limiting their success.
One specific problem has been electrode erosion that becomes an important factor when extended use is required. The need for electrodes can be avoided by the use of inductive type magnetic thrusters which are known to the electric propulsion art. One particular design incorporates a single-turn, flat, spiral induction coil. In that design, multiple parallel connected, single-turn coil sections, that spiral inward from the outside diameter of the annular coil to the inner diameter, are placed on one side of the inductor, with radial current return sections located on the other side of the inductor to form a complete coil. A large number of coils are connected in parallel for low coil parasitic inductance. Capacitors, with spark-gap switches, are inserted at some point in the loop to drive short pulses of electric current, using techniques known to those skilled in the art. A master trigger generator is used to synchronize firing of all of the capacitors. A desirable propellant gas is injected against the coil, which when energized by the capacitor discharge becomes electrically conducting. The magnetic force acting on the electrically conducting propellant generates the rocket engine thrust.
This prior art inductive design still suffers from a number of drawbacks preventing it from being an effective means for long term space travel. What is lacking in this design, and thus is needed, is an inductive type magnetic thruster which utilizes a long life propellant injection valve having better propellant placement for closer inductive coil coupling with the plasma propellant; an electric thruster circuit capable of producing a large initial electric field for efficient ionization; a low parasitic inductance; and the use of solid state switches for improved thruster efficiency and long life mission capability. Of particular importance for the practical implementation of such an improved thruster in a spacecraft electric propulsion system is a coil concept that permits the voltage requirements of the thruster to be met with existing generator technology without requiring the additional mass inherent in the thruster power conditioner. It is an object of this invention to provide for a pulsed inductive thruster which meets the thruster's requirements for effective ionization and efficient thrust generation without requiring special power conditioning for voltage transformation, voltage regulation or filtering.